Bit error ratio

In telecommunication, bit error ratio (BER) is the number of erroneous bits divided by the total number of bits transmitted, received, or processed over some stipulated period.

Note 1: Examples of bit error ratio are (a) transmission BER, i.e., the number of erroneous bits received divided by the total number of bits transmitted; and (b) information BER, i.e., the number of erroneous decoded (corrected) bits divided by the total number of decoded (corrected) bits.

Note 2: The BER is usually expressed as a coefficient and a power of 10; for example, 2.5 erroneous bits out of 100,000 bits transmitted would be 2.5 out of 10⁵ or 2.5 × 10^-5.

Note 3: On good connections you have an BER above 10E-9. The test time for a 95% confidence Level on a:
STM-256 / OC-768 = 1 sec
STM-64 / OC-192 = 3 sec
STM-16c / OC-48c = 12 sec
STM-4c / OC-12c = 48 sec
STM-1 / OC-3 = 3.2 minutes

Source: from Federal Standard 1037C and from MIL-STD-188